Digitally calibrated voltage regulators for power management

ABSTRACT

A computer provides a graphical user interface for displaying a virtual representation of a voltage regulator and for accepting a user requirement for the voltage regulator. The computer automatically determines an internal calibration setting of the voltage regulator that meets the user requirement. The computer simulates operation of the voltage regulator as calibrated with the internal calibration setting. The internal calibration setting is downloaded to the voltage regulator. A calibration controller of the voltage regulator receives the internal calibration setting and outputs digital calibration bits in accordance with the internal calibration setting. The digital calibration bits works in conjunction with interface circuits to adjust circuits of a voltage regulator core to digitally calibrate the voltage regulator.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. ProvisionalApplication No. 61/712,659, filed on Oct. 11, 2012, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to power management, and moreparticularly but not exclusively to voltage regulators.

2. Description of the Background Art

Power management for electronic devices, such as computers, mobilephones, digital music players, and the like, involves the use of avoltage regulator to provide a tightly regulated supply voltage. Apopular voltage regulator employed in electronic devices is a DC-DC(direct current-to-direct current) converter. The DC-DC converter isprovided by its vendor in integrated circuit (IC) form. To save ondesign and manufacturing costs, as well as to shorten time to market,the DC-DC converter is designed to operate in a variety of conditions tomeet different customer requirements. For each customer or application,a DC-DC converter thus needs to be manually calibrated to meetparticular user requirements, such as, for example, output voltage andswitching frequency. The manual calibration procedure is not trivial,and typically requires electrical engineers with experience in powermanagement and in using the particular DC-DC converter.

SUMMARY

In one embodiment, a computer provides a graphical user interface fordisplaying a virtual representation of a voltage regulator and foraccepting a user requirement for the voltage regulator. The computerautomatically determines an internal calibration setting of the voltageregulator that meets the user requirement. The computer simulatesoperation of the voltage regulator as calibrated with the internalcalibration setting. The internal calibration setting is downloaded tothe voltage regulator. A calibration controller of the voltage regulatorreceives the internal calibration setting and outputs digitalcalibration bits in accordance with the internal calibration setting.The digital calibration bits works in conjunction with interfacecircuits to adjust circuits of a voltage regulator core to digitallycalibrate the voltage regulator.

These and other features of the present invention will be readilyapparent to persons of ordinary skill in the art upon reading theentirety of this disclosure, which includes the accompanying drawingsand claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a computer in accordance with anembodiment of the present invention.

FIG. 2 schematically illustrates operation of a system for digitallycalibrating a voltage regulator in accordance with an embodiment of thepresent invention.

FIG. 3 shows a flow diagram of a method of digitally calibrating avoltage regulator in accordance with an embodiment of the presentinvention.

FIG. 4 shows a schematic diagram of a digitally calibrated voltageregulator in accordance with an embodiment of the present invention.

FIG. 5 shows a schematic diagram of an example voltage regulator core inaccordance with an embodiment of the present invention.

FIG. 6 shows a schematic diagram of a calibration controller inaccordance with an embodiment of the present invention.

FIG. 7 shows a schematic diagram of a digitally settable referencecircuit in accordance with an embodiment of the present invention.

FIG. 8 shows a schematic diagram of a loop control module in accordancewith an embodiment of the present invention.

FIG. 9 shows a schematic diagram of a ramp generator in accordance withan embodiment of the present invention.

FIG. 10 shows a schematic diagram of a clock generator in accordancewith an embodiment of the present invention.

FIG. 11 shows a schematic diagram of an example protection circuit inaccordance with an embodiment of the present invention.

The use of the same reference label in different drawings indicates thesame or like components.

DETAILED DESCRIPTION

In the present disclosure, numerous specific details are provided, suchas examples of electrical circuits, components, and methods, to providea thorough understanding of embodiments of the invention. Persons ofordinary skill in the art will recognize, however, that the inventioncan be practiced without one or more of the specific details. In otherinstances, well-known details are not shown or described to avoidobscuring aspects of the invention.

FIG. 1 shows a schematic diagram of a computer 100 in accordance with anembodiment of the present invention. The computer 100 may be employed bya user, who is typically an electrical engineer, to digitally calibratea voltage regulator to meet particular user requirements. The computer100 may have fewer or more components without detracting from the meritsof the present invention.

In the example of FIG. 1, the computer 100 includes a processor 101 andone or more buses 103 coupling its various components. The computer 100may include one or more user input devices 102 (e.g., keyboard, mouse),one or more data storage devices 106 (e.g., hard drive, optical disk,Universal Serial Bus memory), a display monitor 104 (e.g., liquidcrystal display, flat panel monitor, cathode ray tube), a computernetwork interface 105 (e.g., network adapter, modem), and a main memory108 (e.g., random access memory). The computer network interface 105 maybe coupled to a computer network 109.

In the example of FIG. 1, the computer 100 includes an input/output(I/O) bus interface 112. The I/O bus interface 112 may comprise auniversal serial bus (USB) interface, for example. A digitallycalibrated voltage regulator (“DCVR”) 114 may be coupled to the computer100 by way of the I/O bus interface 112. For example, the voltageregulator 114 may be mounted to a circuit board 115 (e.g., powermanagement board, fixture, calibration board) that converts USBcommunications to I2C bus communications supported by the voltageregulator 114.

The computer 100 is a particular machine as programmed with softwaremodules, which in the example of FIG. 1 includes a virtual bench 117, aknowledge base 118, and a simulation engine 119. The aforementionedsoftware modules comprise computer-readable program code storednon-transitory in the main memory 108 for execution by the processor101. The computer 100 may be configured to perform its functions byexecuting the software modules. The software modules may be loaded fromthe data storage device 106 to the main memory 108. An article ofmanufacture may be embodied as computer-readable storage mediumincluding instructions that when executed by a computer causes thecomputer to be operable to perform the functions of the softwaremodules.

The virtual bench 117 may comprise computer-readable program code thatprovides a graphical user interface (GUI) for digitally calibrating thevoltage regulator 114. In one embodiment, the digital calibrationinvolves adjusting a circuit of a voltage regulator core of the voltageregulator 114 to set electrical values (e.g., resistance, capacitance,reference voltage, threshold voltage) in the voltage regulator. Theselection of electrical values does not necessarily change the topologyof the voltage regulator. In one embodiment, the selection of electricalvalues changes operating characteristics of the voltage regulator tooptimize the operation of the voltage regulator to meet particularrequirements, such as output voltage, switching frequency, and othercharacteristics typically changeable in a voltage regulator by manualselection of electrical values and manual installation of additionalcomponents. Depending on the application, in other embodiments, thecalibration may also involve changing the topology of the voltageregulator.

The virtual bench 117 may provide graphical elements that virtuallyrepresent test and measurement instruments typically employed by anelectrical engineer in calibrating a voltage regulator, includingmeters, oscilloscopes, power supply, and the like. The virtual bench 117may provide a virtual representation of the voltage regulator beingcalibrated, and also display data pertaining to the calibration,including Bode plots, for example. The virtual bench 117 may beimplemented using conventional programming methodology, including objectoriented programming techniques. The virtual bench 117 may receive userrequirements for the voltage regulator being calibrated including outputvoltage, switching frequency, protection thresholds, and other userrequirements. The requirements may be entered by the user by selectingcomponents, electrical values, output voltage, switching frequency, andother parameters in the virtual bench 117.

The simulation engine 118 may comprise computer-readable program codethat simulates the operation of a voltage regulator that is virtuallyrepresented by the virtual bench 117. The simulation engine 118 maysimulate the operation of the voltage regulator by receiving the userrequirements from the virtual bench 117, and determining the resultingbehavior of the voltage regulator when operated in accordance with theuser requirements. The simulation engine 118 may determine the resultingbehavior and characteristics of the voltage regulator using equations,tabular data, and other application design guidelines for the voltageregulator.

The application design guidelines for a voltage regulator may beincorporated in the knowledge base 118. The knowledge base 118 may be anexpert system, for example. The knowledge base 118 may reflect theknowledge of experts in the voltage regulator, including knowledge ofits designers and vendor field application engineers. The applicationdesign guidelines indicate the effect of particular component,electrical value, switching frequency, output voltage, start-up time,protection thresholds, or other parameter to the operation of thevoltage regulator. The simulation engine 118 may consult with theknowledge base 118 to determine the resulting operation of the voltageregulator for particular selections. The knowledge base 118 may alsogenerate or retrieve internal calibration settings for digitallycalibrating the voltage regulator to meet particular user requirements.The internal calibration settings may be in the form of calibration bitsthat adjust circuits of the voltage regulator 114.

As a particular example, the output voltage of the voltage regulator 114may be changed by appropriate selection of a reference voltage value.The vendor, i.e., the maker of the voltage regulator 114, provides anequation relating the reference voltage value to output voltage. Thisequation may be incorporated in the knowledge base 118. The user mayenter his desired output voltage in the virtual bench 117. Thesimulation engine 119 receives the desired output voltage, consults theknowledge base 118 to determine the corresponding reference voltagevalue, and simulates operation of the voltage regulator 114 ascalibrated with the reference voltage value. The voltage regulator 114may be subsequently digitally calibrated to have the reference value byreceiving and effecting internal calibration settings, such as digitalcalibration bits that adjust a reference voltage generator circuit inthe voltage regulator 114 to output the reference voltage value.

The knowledge base 118 may be periodically updated to incorporate bugfixes, add new features, include additional voltage regulators, and forother reasons. In one embodiment, an update for the knowledge base 118is received by the computer 100 from a remote server computer over theInternet.

FIG. 2 schematically illustrates operation of a system for digitallycalibrating a voltage regulator in accordance with an embodiment of thepresent invention. In the example of FIG. 2, the computer 100 is runningthe virtual bench 117, which displays a graphical user interface (seearrow 170). In the example of FIG. 2, the virtual bench 117 displaysvirtual representations of a power supply 151, a voltage regulator 152,an oscilloscope 153, an output inductor 155, output capacitor 156, and avirtual load 157. The voltage regulator 152 is a virtual representationof a digitally calibrated voltage regulator 114. Accordingly, in thisexample, the knowledge base 118 includes the application designguidelines of the voltage regulator 114. The voltage regulator 114 maybe provided in integrated circuit (“IC”) form.

The virtual components displayed by the virtual bench 117 may bemanipulated on-screen by the user, e.g., using a mouse. The user mayenter user requirements into the virtual bench 117 by selecting valuesfor different parameters of the voltage regulator 114. The simulationengine 119 receives the user requirements (see arrow 171), consults theknowledge base 118 to determine the expected operation of the voltageregulator 114 as operated to meet the user requirements (see arrows 172and 173), and reflects the expected operation of the voltage regulator114 in the virtual bench 117 (see arrow 174).

The simulation engine 119 may also receive internal calibration settingsfrom the knowledge base 118. The internal calibration settings mayreflect component selections and other adjustments that need to be madein the voltage regulator 114 to operate as specified by the user in thevirtual bench 117. The internal calibration settings may be in the formof digital calibration bits that when presented to the voltage regulator114 calibrates the voltage regulator 114 in accordance with the userrequirements.

As a particular example, the user may attach the virtual oscilloscope153 on the output voltage Vout on the virtual load 157 to see thesimulated output voltage waveform as determined by the simulation engine119, resulting from selected values of the output inductor 155 andoutput capacitor 156. The virtual bench 117 may provide resultinggraphical data 154, such as Bode plots, for example.

The user may initiate digital calibration of the voltage regulator 114after he is satisfied with its simulated operation. To do so, the usermay install the voltage regulator 114 in a calibration board 160 orother circuit board or fixture. In one embodiment, the virtual bench 117stores the internal calibration settings for digitally calibrating thevoltage regulator 114 in accordance with the selections made by the userin the virtual bench 117. For example, the virtual bench 117 may receivethe internal calibration settings from the simulation engine 119, whichreceives the internal calibration settings from the knowledge base 118.When the user initiates digital calibration, e.g., by clicking on anicon on the virtual bench 117, the virtual bench 117 may download theinternal calibration settings to the voltage regulator 114. In theexample of FIG. 2, the internal calibration settings are transferredfrom the computer 100 to the voltage regulator 114 over a USB 175. Thecalibration board 160 converts signals of the USB 175 to I2C bus 176compatible signals, which are received by the voltage regulator 114. Thevoltage regulator 114 performs calibration in accordance with theinternal calibration settings. The internal calibration settings maycomprise digital calibration bits that select and deselect components inthe voltage regulator 114 to select electrical values, such asresistance and capacitance, to make the voltage regulator operate asspecified by the user in the virtual bench 117. The digital calibrationbits may also set reference voltages, threshold values, programmableclock frequencies, etc. As a particular example, the calibration bitsmay configure a digital-to-analog converter (DAC) in the voltageregulator 114 to output a reference voltage Vr to adjust the outputvoltage Vout to a value specified by the user in the virtual bench 117.

In the example of FIG. 2, the voltage regulator 114 is installed in apower management board 180 after digital calibration (see arrow 177). Ascan be appreciated, in other embodiments, the voltage regulator 114 mayalso be digitally calibrated while installed in the power managementboard 180 instead of in the calibration board 160.

In the example of FIG. 2, the power management board 180 comprises aprocessor 181 and a plurality of digitally calibrated voltage regulators114 (i.e., 114-1, 114-2, . . . , 114-n). The processor 181 may comprisea microprocessor or a microcontroller, for example. Other components ofthe power management board not necessary to understand the presentinvention are not shown or described in the interest of clarity. In theexample of FIG. 2, the power management board 180 includes an I/O bus inthe form of an I2C bus 182. A voltage regulator 114 may communicate withthe processor 181 over the bus 182. In one embodiment, a voltageregulator 114 reports internal conditions, such as output voltage,junction temperature, output current, etc., to the processor 181 forremote monitoring. As a particular example, the voltage regulator 114may include an analog-to-digital converter (ADC) that converts outputvoltage to digital form for reporting to the processor 181. The powermanagement board 180 is subsequently installed in an end product 185,such as a consumer electronic device (see arrow 178). The end product185 may be a mobile phone, portable media player, tablet, computer, orother electronic devices.

FIG. 3 shows a flow diagram of a method of digitally calibrating avoltage regulator in accordance with an embodiment of the presentinvention. The method of FIG. 3 is explained using the components shownin FIG. 2 for illustration purposes only.

In the example of FIG. 3, the virtual bench 117 receives userrequirements, such as output voltage and switching frequency, for adigitally calibrated voltage regulator 114 (step 191). The virtual bench117 passes the user requirements to the simulation engine 119, whichconsults with the knowledge base 118 to automatically determine internalcalibration settings for the voltage regulator 114 that meet the userrequirements (step 192). The internal calibration settings may be in theform of calibration bits that select electrical values or components tocalibrate circuits of the voltage regulator 114. For example, theinternal calibration settings my enable or disable (e.g., by opening orclosing) switch elements in the voltage regulator 114. The simulationengine 119 simulates the operation of the voltage regulator 114 ascalibrated with the internal calibration settings (step 193). Theprocess of receiving user requirements, determining the correspondinginternal calibration settings, and simulating the operation of thevoltage regulator 114 with the internal calibration settings is repeateduntil the user is satisfied with the simulated operation of the voltageregulator 114 (step 194). Thereafter, the internal calibration settingsare downloaded to the voltage regulator, for example as mounted in thecalibration board 160 or in the power management board 180 (step 195).The voltage regulator 114 is then installed in the applicationenvironment, which may be the end product 185 (step 196).

Referring now to FIG. 4, there is shown a schematic diagram of adigitally calibrated voltage regulator 114 in accordance with anembodiment of the present invention. The voltage regulator 114 may bepackaged as an IC. In the example of FIG. 4, the voltage regulator 114comprises a digital calibration controller 250, a plurality of interfacecircuits 251, and a voltage regulator core comprising a DC-DC converter252. The DC-DC converter 252 comprises a step-down DC-DC converter thatconverts an input voltage Vin to a tightly regulated output voltageVout. In other embodiments, the DC-DC converter 252 is replaced withother voltage regulators, including a step up DC-DC converter.

The calibration controller 250 may comprise electrical circuitry thatreceives internal calibration settings over an external I/O bus 254 andoutputs digital calibration bits in accordance with the internalcalibration settings. The digital calibration bits may be applied to theDC-DC converter 252 by way of the interface circuits 251. Thecalibration controller 250 may also receive internal operatingconditions of the voltage regulator 114 and provide the internaloperating conditions to an external circuit that performs remotemonitoring, such as the processor 181 of the power management board 180,for example.

The interface circuits 251 may comprise one or more electrical circuitsthat provide hooks for calibrating the voltage regulator 114 inaccordance with digital calibration bits received from the calibrationcontroller 250. The interface circuits 251 may set a setting of thevoltage regulator in accordance with the digital calibration bits. Inone embodiment, the interface circuits 251 convert digital calibrationbits to electrical values in the voltage regulator 114. As a particularexample, the interface circuits 251 may comprise digitally controlledswitch elements for selecting and deselecting components to changeelectrical values, such as capacitance and resistance that adjust gains,poles, zeros, and other parameters of the voltage regulator 114. Theswitch elements may comprise transistors that are switched on or off toopen or close. A switch element across a component may be closed toshort the component out of a circuit, or opened to add the component tothe circuit. A switch element in series with a component may be openedto remove the component from the circuit, or closed to add the componentto the circuit. The interface circuits 251 may also compriseprogrammable components and components that convert digital calibrationbits to electrical values. For example, the interface circuits 251 maycomprise DACs, programmable clocks, and the like.

FIG. 5 shows a schematic diagram of an example voltage regulator core inthe form of the DC-DC converter 252 in accordance with an embodiment ofthe present invention. It is to be noted that the DC-DC converter 252 isprovided merely to provide an illustrative example, and not as alimitation.

In the example of FIG. 5, the DC-DC converter 252 receives the inputvoltage Vin and generates the regulated step-down output voltage Vout bycontrolling the switching of the transistors M1 and M2. The feedbackcontrol loop of the DC-DC converter 252 includes an output voltagesensing circuit in the form of a resistive divider comprising resistorsR1 and R2. The resistive divider provides a sensed output voltageindicative of the output voltage Vout to a loop control module 201,which in one embodiment comprises a transconductance amplifier 208 and aloop filter comprising a resistor R3 and a capacitor C1. Thetransconductance amplifier 208 compares the sensed output voltage to areference voltage Vr. The resistor R3 and the capacitor C1 serve aproportional-integral-derivative (PID) function on the output of thetransconductance amplifier 208, which is summed with a ramp referencesignal generated by a ramp generator 203. The resulting ramp signal atthe output of the summer is presented to a pulse-width-modulation (PWM)module 209 comprising a PWM amplifier 204 and a gain block 210. The PWMmodule 209 receives a sensed output current Io, which may be amplifiedby the gain block 210 having a resistance Ri to convert the sensedoutput current Io to a voltage value that may be compared to the rampsignal. The PWM amplifier 204 compares the sensed output current Io tothe ramp signal to control when to turn OFF the transistor M1 and turnON the transistor M2. A clock generator 206 generates a clock signalthat periodically turns ON the transistor M1 and turns OFF thetransistor M2. The clock signal controls the switching frequency of thevoltage regulator 114. The outputs of the clock generator 206 and thePWM amplifier 204 are input to a flip-flop 205, which drives thetransistors M1 and M2.

In the example of FIG. 5, the output voltage Vout may be calibrated tomeet user requirements by changing the value of the reference voltage Vrpresented to the transconductance amplifier 208. The reference voltageVr may be provided by a digitally settable reference voltage generator202. The reference voltage generator 202 may receive digital calibrationbits (DCB) 211 from the calibration controller 250, and set the value ofthe reference voltage Vr in accordance with the digital calibration bits211 to generate an output voltage Vout specified by the user in thevirtual bench 117.

The loop control module 201 may receive digital calibration bits 212from the calibration controller 250. The loop control module 201 mayadjust the equivalent resistance of the resistor R3, equivalentcapacitance of the capacitor C1, the gain of the transconductanceamplifier 208, and other electrical values that are settable in thecontrol module 201 in accordance with the digital calibration bits 212to set poles, zeros, and other parameters in accordance with userrequirements entered in the virtual bench 117.

The ramp generator 203 may receive digital calibration bits 213 from thecalibration controller 250. The ramp generator 203 may adjust the slopeand other parameters of its output ramp reference signal in accordancewith the digital calibration bits 213 to meet user requirements enteredin the virtual bench 117.

The clock generator 214 may receive digital calibration bits 214 fromthe calibration controller 250. The clock generator may change thefrequency and other parameters of its output clock signal in accordancewith the digital calibration bits 214 to set the switching frequency ofthe voltage regulator 114 as specified by the user in the virtual bench117.

The voltage regulator 114 may further include protection circuits 207,such as an under voltage lockout (UVLO) circuit, over voltage protectioncircuit, over current protection circuit, and other protection circuitstypically provided in a voltage regulator. The protection circuits 207may perform their function by receiving sensed output voltage, sensedinput voltage, sensed output current, and other signals that aremonitored. The thresholds (e.g., TH1, TH2, TH3, etc.) for triggering theprotection circuits may be set by corresponding digital calibration bits402 from the calibration controller 250 in accordance with userrequirements entered in the virtual bench 117.

FIG. 6 shows a schematic diagram of the calibration controller 250 inaccordance with an embodiment of the present invention. In the exampleof FIG. 6, the calibration controller 250 includes an I/O bus interface253 that performs serial to parallel conversion. In one embodiment, theI/O bus interface 253 communicates with a serial external I/O bus 254comprising an I2C bus. The calibration controller 250 may communicateover the external I/O bus 254 to receive internal calibration settingsfrom the computer 100. The calibration controller 250 may alsocommunicate over the external I/O bus 254 to send remote monitoringsignals to the processor 181 of the power management board 180.Components of the calibration controller 250 that are not necessary tothe understanding of the present invention, such as clocks, glue logic,and internal buffers, are not shown in the interest of clarity. Thecomponents of the calibration controller 250 may communicate over aninternal bus 287.

In one embodiment, the calibration controller 250 includes a controllerin the form of a state machine 280. The state machine 280 may beimplemented using a gate array, flip-flops, programmable logic, andother logic means. The state machine 280 may also be implemented using amicrocontroller, microprocessor, digital signal processor, or otherprocessor depending on cost considerations.

The state machine 280 may be configured to receive an internalcalibration setting over the I/O bus interface 253, and sequence througha series of predetermined states to output corresponding digitalcalibration bits in accordance with the internal calibration settings.In one embodiment, the state machine 280 sends out the correspondingdigital calibration bits over the internal bus 287 to one or moredigital output ports 285. A digital output port 285 may be coupled toone or more components of an interface circuit 251. As can beappreciated, the state machine 280 does not need much computing powerbecause most of the processing in determining which digital calibrationbits need to be selected (e.g., set to logic HIGH) or deselected (e.g.,set to logic LOW) may be performed by the virtual bench 117, knowledgebase 118, and simulation ancient 119 in the computer 100. The statemachine 280 simply needs to cycle through predetermined states to selectand deselect digital calibration bits as indicated in the receivedinternal calibration settings.

The calibration controller 250 may be configured to provide remotemonitoring functions. In the example of FIG. 6, the calibrationcontroller 250 receives sensed voltage, current, temperature, or othermonitored condition in the voltage regulator 114 by way of themultiplexer 286. The selected sensed condition is output by themultiplexer 286 to the input of an ADC 283, which converts the sensedcondition to digital form suitable for transmission to an externalprocessor, such as the processor 181 of the power management board 180.For example, the state machine 280 may receive a request from theprocessor 181 to provide the present value of a sensed condition, suchas the output voltage (Vout), output current (Io), or a junctiontemperature (Tj). In response to the request, the state machine 280 maycycle through predetermined states to select the particular sensedcondition from the input of the multiplexer 286, to retrieve the digitalvalue of the sensed condition from the ADC 283, and to transfer thedigital value of the sensed condition to the processor 181 by way of theexternal I/O bus interface 253. The state machine 280 may use the memorystorage space provided by the nonvolatile memory 281 and banks ofregisters 282 as temporary workspace and general storage.

FIG. 7 shows a schematic diagram of the digitally settable referencecircuit 202 in accordance with an embodiment of the present invention.In the example of FIG. 7, the reference circuit 202 comprises a DAC 291having a band gap reference voltage VBG for reference. The DAC 291receives digital calibration bits 211 (i.e., 211-1, 211-2, . . . ,2111-n) from the calibration controller 250 as inputs, and converts thevalue of the digital calibration bits 211 to analog form, which in theexample of FIG. 7 is the reference voltage Vr. The reference voltage Vrmay thus be adjusted by appropriate changes to the digital calibrationbits 211. The reference voltage Vr, which is presented to the input ofthe transconductance amplifier 208, controls the output voltage Vout bybeing compared to the sensed output voltage Vout (see FIG. 5).Accordingly, the digital calibration bits 211 may have a bit patternthat results in a particular output voltage Vout specified by the user.

FIG. 8 shows a schematic diagram of the loop control module 201 inaccordance with an embodiment of the present invention. In the exampleof FIG. 8, the digital calibration bits 212 (i.e., 212-1, 212-2, etc.),which are received by the control module 201 from the calibrationcontroller 250, controls switch elements 304-310. A switch element maycomprise a transistor or other device that may be closed or openeddepending on a control input, which in this example is a digitalcalibration bit. In the following examples, a logic HIGH digitalcalibration bit closes a switch element and a logic LOW digitalcalibration bit opens the switch element.

In the example of FIG. 8, some of the digital calibration bits 212 areemployed to adjust the gain of the transconductance amplifier 208 bycontrolling the tail current of the transconductance amplifier 208. Inparticular, in the example of FIG. 8, the digital calibration bits212-1, 212, and 212-3 control the opening and closing of the switchelements 304, 305, and 306, respectively. The value of the tail currentof the transconductance amplifier 208, and thus its gain, may beadjusted by adding or removing the current source 301, current source302, and/or the current source 303 to the tail current. For example,setting the digital calibration bit 212-1 to be at logic HIGH closes theswitch element 304 to add the current source 301 to the tail current ofthe transconductance amplifier 208. Similarly, setting the digitalcalibration bit 212-1 to be at logic LOW opens the switch element 304 toremove the current source 301 from the tail current of thetransconductance amplifier 208.

Switch elements may also be employed to add or remove components tochange equivalent component values. For example, resistors R6 and R8 andcapacitors C3 and C4 may be added or removed from the loop controlmodule 201 to change the poles and zeros of the control loop. Morespecifically, the digital calibration bit 212-4 may be set to logic HIGHto close the switch element 307 and thereby, in effect, remove theresistor R6. Setting the digital calibration bit 212-4 to a logic LOWopens the switch element 307 to add the resistance of the resistor R6 inseries with the resistor R5. Similarly, the digital calibration bit212-7 may be set to a logic HIGH or logic LOW to add or remove thecapacitor C4. Particular bit patterns of the digital calibration bits212 may therefore be presented to the control module 201 to adjust thegain of the transconductance amplifier 208 and the poles and zeros ofthe control loop to meet particular requirements. As can be appreciated,the bit patterns of the digital calibration bits 212 for particularrequirements may be generated by the simulation engine 119 inconsultation with the knowledge base 118, received by the calibrationcontroller 250, and output by the calibration controller 250 to the loopcontrol module 201 by way of interface circuits, which in the example ofFIG. 8 comprise switch elements 304-310.

FIG. 9 shows a schematic diagram of the ramp generator 203 in accordancewith an embodiment of the present invention. In the example of FIG. 9,the ramp generator 203 receives digital calibration bits 213 (i.e.213-1, 213-2, etc.) from the calibration controller 250. The bit patternof the digital calibration bits 213 opens and closes the switch elements324-328 to adjust the slope of the ramp reference signal provided at theoutput of the amplifier 329. In particular, the switch elements 324-326may be controlled by the digital calibration bits 213-1, 213-2, and213-3 to add or remove the current sources 321 322, and 323,respectively. The switch elements 327 and 328 may be controlled by thedigital calibration bits 213-4 and 213-5 to add or remove the capacitorsC6 and C7, respectively. The amplifier 329 compares the resulting signalto a bandgap voltage VBG to generate the ramp reference signal.Particular bit patterns of the digital calibration bits 213 maytherefore be presented to the ramp generator 203 to adjust the slope ofthe ramp reference signal to meet particular requirements.

FIG. 10 shows a schematic diagram of the clock generator 206 inaccordance with an embodiment of the present invention. In the exampleof FIG. 10, the clock generator 206 is a programmable clock generatorthat receives digital calibration bits 214 (i.e., 214-1, 214-2, . . . ,214-n) from the calibration controller 250. The clock generator 206outputs a clock signal having a frequency dictated by the digitalcalibration bits 214. Accordingly, the clock signal, and therefore theswitching frequency of the voltage regulator 114, may be set to meetparticular requirements by providing a particular bit pattern to theinputs of the clock generator 206.

FIG. 11 shows a schematic diagram of an example protection circuit 207in accordance with an embodiment of the present invention. In general, aprotection circuit 207 may include a comparator 404 for comparing asensed parameter to a threshold. The threshold may be calibrated bypresenting a bit pattern of the digital calibration bits 402 (i.e.,402-1, 402-2, . . . , 402-n) received from the calibration controller250 to the inputs of a DAC 401, which outputs a corresponding thresholdvalue. The output of the DAC 401 may be scaled or pre-processed (e.g.,converted to current or voltage) by a pre-processing block 403 beforebeing presented to the comparator 404. The comparator 404 may be avoltage or current comparator depending on the sensed parameter. Forexample, assuming the protection circuit 207 is an overvoltageprotection circuit, the sensed parameter may comprise output voltage andthe comparator 404 may be a voltage comparator. The pre-processing block403 may be a gain or divider block to scale the output of the DAC 401.The pre-processing block 403 may also be omitted in that case.

As another example, assuming the protection circuit 207 is anovercurrent protection circuit, the sensed parameter may comprise outputcurrent and the comparator 404 may comprise a current comparator. Thepre-processing block 403 may comprise a voltage to current converter toconvert the output of the DAC 401 to a current output. Alternatively,the comparator 404 may receive the sensed parameter as a voltageindicative of output current (e.g., voltage drop of the output currenton a resistor). In that case, the sensed parameter is compared to athreshold voltage set by the output of the DAC 401 in accordance withthe bit pattern of the input digital calibration bits 402.

Digitally calibrated voltage regulators and methods for using same havebeen disclosed. While specific embodiments of the present invention havebeen provided, it is to be understood that these embodiments are forillustration purposes and not limiting. Many additional embodiments willbe apparent to persons of ordinary skill in the art reading thisdisclosure.

What is claimed is:
 1. A voltage regulator integrated circuit (IC) comprising: a calibration controller that receives an internal calibration setting over an external input/output (I/O) bus, and outputs digital calibration bits in accordance with the internal calibration setting; an interface circuit that receives the digital calibration bits, and sets a setting of the voltage regulator in accordance with the digital calibration bits; and a voltage regulator core that converts an input voltage to a regulated output voltage.
 2. The voltage regulator of claim 1 wherein the voltage regulator core comprises a step down DC-DC converter.
 3. The voltage regulator of claim 1 wherein the interface circuit comprises a switch element that selects and deselects a component in the voltage regulator core.
 4. The voltage regulator of claim 1 wherein the external I/O bus is a serial bus and the calibration controller performs serial to parallel bus conversion.
 5. The voltage regulator of claim 1 wherein the interface circuit comprises a switch element that opens or closes in accordance with a bit in the digital calibration bits.
 6. The voltage regulator of claim 1 wherein the calibration controller receives the internal calibration setting from a computer that provides a graphical interface to a user, the graphical interface displaying a virtual representation of the voltage regulator.
 7. A system for digitally calibrating a voltage regulator, the system comprising: a computer comprising a memory and a processor configured to execute computer-readable program code in the memory, the computer displays a virtual representation of a voltage regulator, receives a user requirement for the voltage regulator, automatically determines an internal calibration setting to meet the user requirement, and simulates operation of the voltage regulator with the internal calibration setting; and the voltage regulator, the voltage regulator receives the internal calibration setting over an external input/output (I/O bus) coupled to the computer, and calibrates an internal circuit in accordance with the internal calibration settings.
 8. The system of claim 7 further comprising: a calibration board that receives the internal calibration setting and provides the internal calibration setting to a calibration controller of the voltage regulator over the external I/O bus.
 9. The system of claim 7 wherein the computer further comprises an I/O bus interface coupled to an I/O bus interface of the voltage regulator.
 10. The system of claim 9 wherein the I/O bus interface of the computer comprises a universal serial bus (USB).
 11. The system of claim 10 wherein the computer includes a graphical user interface that receives the user requirement.
 12. The system of claim 11 wherein the graphical user interface provides a virtual bench that displays the virtual representation of the voltage regulator. 